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Unformatted text preview: for data networks, we can consider the arrival rate to be in packets/sec. Let N t = number of packets in the link at time t Q – What is the average number of packets in the link? N = tlim E fN tg =
!1 1
X
jj = 1 , = , :
j =0 Thus, using the steadystate probabilities, we can obtain the result for N . What about other measures
such as average packet delay?
To obtain this, we need the use the following result known as Little’s Law : CS 522, v 0.94, d.medhi, W’99 12 avg. number of packets in system in steady state (N)
= avg. arrival rate * avg. packet delay in system
in steady state (T)
That is, N = T: Rearranging, we get 1
T = N= = , = 1 , :
Average waiting time in the queue, W , is
W= Avg. waiting time in System – Avg. waiting time in Service 1
1
= , , = , : Again, by Little’s Law which is also applicable in queues, the average number of customers in queue is,
2 Nq = W = 1 , :
Thus, we have shown above four performance measures that may be of interest for a network l...
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 Fall '08
 Staff
 Computer Networks

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